The present invention relates generally to electronic systems. More particularly, the invention relates to an electromagnetic interference (EMI) reduction device.
A trend in the electronics industry is to generate smaller and faster electronic devices. As a result, these devices consume more power and hence, produce more heat. Excessive heat can cause significant damage to an electronic device thereby reducing its life. For this reason, various techniques are employed to eliminate or dissipate the heat generated from the electronic device. A heat sink is one such technique. A heat sink is thermally coupled to the electronic device and as such, allows the heat to flow from the electronic device through the heat sink to the surrounding open space.
In addition, the operation of these electronic devices is accompanied by the generation of electromagnetic radiation or energy. The emissions of the electromagnetic radiation can cause significant electronic interference or noise with other surrounding electronic circuitry. To reduce such disturbances, the source of these emissions is usually suppressed. However, the EMI suppression problem is further complicated when the electronic device is coupled to a heat sink. The heat sink acts as an antenna for the EMI energy thereby increasing the EMI emissions.
A common solution for suppressing EMI energy is to ground the heat sink. FIG. 1 illustrates an exemplary grounded heat sink. There is shown a heat sink 100 coupled to a grounded electronic device 102 that is mounted onto a printed circuit board (PCB) 104. In this example, the grounded electronic device 102 is a processor core having a silicon logic die 106. A thermal compound 108, such as a dielectric material, is placed between the heat sink 100 and the grounded electronic device 102 so that thermal contact is maintained and the heat generated by the device 102 is transferred to the heat sink 100.
Mounting fences 110 are positioned on four opposite sides of the PCB 104 in order to ground the heat sink 100. The mounting fences 110 are attached to the heat sink 100 and the PCB 104, which acts in this case as a ground plane. The mounting fences 110 provide a Faraday shield around the device 102 in order to shield the EMI energy generated from the clock circuitry internal to the processor 102 from effecting adjacent components and from releasing EMI energy outside of the heat sink 100.
Additional EMI suppression is provided by four sets of grounding pads 112a-112d on the PCB 104 that surround the processor 102, as shown in FIG. 2. The grounding pads 112 minimize or ground EMI noise generated by the switching of all the component pins under maximum capacitive load. Thus, the combination of the grounding pads and the grounded heat sink dissipates the heat from the processor core and grounds the EMI energy generated by the processor core.
As the internal clock speed of processors increase, these processors will require more extensive EMI reduction or grounding. In some cases, the grounded heat sink approach may not be suitable to effectively eliminate the EMI emissions since this approach has a longer grounding path. As such, grounding may need to be performed closer to the silicon logic die in order to create a shorter grounding path that effectively reduces the EMI energy emanating from the processor core.
Accordingly, there is a need for an EMI reduction technique that can minimize or eliminate EMI energy generated from a processor core closer to the source of the emissions and in such a manner that is cost efficient and easy to manufacture.
The present invention pertains to a mechanism for reducing EMI emissions generated from electronic components that are mounted on a PCB. In a first embodiment, the PCB is part of an electronic assembly that is mounted into a connector resident on a motherboard. The electronic assembly can be a processor module that includes a PCB and an electrically-conductive thermal plate that is capacitively coupled to the PCB. The PCB has a processor core that is the source of unwanted electromagnetic emissions. As such, a grounding mechanism or device is provided to reduce these emissions more effectively.
The grounding device is formed of a metallic spring material and includes a frame having a number of mounting tabs and spring contact fingers. The mounting tabs are used to affix the grounding device in a desired position relative to a connector on the motherboard and to maintain electrical contact with the ground plane of the motherboard. A number of mounting holes are made on the motherboard near the connector and extend through the thickness of the motherboard. Each mounting tab is soldered to a respective mounting hole thereby providing an electrical connection to the ground plane of the motherboard. The spring contact fingers are used to maintain a pressure contact between the connector and the thermal plate when the processor module is placed into the connector.
The grounding device is mounted onto the motherboard so that the grounding device is coupled to the connector. When force is applied to insert the processor module into the connector, the thermal plate slides on the outer surface of the grounding device which forces the spring contact fingers to deflect. The deflected spring contact fingers apply pressure against the thermal plate which causes the thermal plate to maintain a physical and electrical connection to the grounding device.
The grounding device has several benefits. First, it provides a short ground path from the source of the electromagnetic emissions to the ground plane. As a result of this shorter grounding path, the grounding device is more effective at reducing the electromagnetic emissions generated from the processor module. In addition, the grounding device is external to the connector which makes it easy to adapt it to various connector designs. Additionally, the grounding device offers a grounding reference plane which improves the signal integrity characteristics of the connector contacts by maintaining a more stable transmission line characteristic.